This invention relates to a process that comprises reacting CFX2CFXI, wherein each X is independently F or Cl, provided that at least one X is Cl and at least one X is F, with an aromatic compound Ar to form (CFX2CFX)nxe2x80x94Ar, wherein n is 1, 2 or 3. This product may then be dechlorohalogenated to form (CFX=CF)nxe2x80x94Ar.
Polymers of various xcex1,xcex2,xcex2-trifluorostyrenes are used to fabricate ion-exchange membranes and solid polymer electrolytes for use in electrochemical applications such as fuel cells. Polymers containing monomer units based on xcex1,xcex2,xcex2-trifluorostyrene sulfonic acid (I) are typically used. Polymers containing monomer units based on other xcex1,xcex2,xcex2-trifluorostyrene derivatives are also used. See U.S. Pat. Nos. 4,012,303, 4,107,005 (division) and 4,113,922 (division); and U.S. Pat. No. 5,422,411, 5,498,639 (continuation), U.S. Pat. No. 5,602,185 (CIP), U.S. Pat. No. 5,684,192 (division of CIP) and U.S. Pat. No. 5,773,480 (CIP). 
Hodgdon, Polyelectrolytes Prepared from Perfluoroalkylaryl Macromolecules, J. Polymer Sci., 6:171-191 (1968) (xe2x80x9cHodgdonxe2x80x9d) discloses a many-step synthesis of xcex1,xcex2,xcex2-trifluorostyrene starting from trifluoroacetophenone and Grignard reagent phenyl magnesium bromide, followed by polymerization of the monomer and partial sulfonation of the resulting poly-xcex1,xcex2,xcex2-trifluorostyrene. U.S. Pat. Nos. 5,602,185 and 5,684,192 (division) disclose a many-step synthesis of p-sulfonyl fluoride-xcex1,xcex2,xcex2-trifluorostyrene via p-iodobenzenesulfonylfluoride. U.S. Pat. No. 3,449,449 discloses a synthesis of xcex1,xcex2,xcex2-trifluorostyrene from phenyl sodium and tetrafluoroethylene. U.S. Pat. No. 3,489,807 discloses pyrolytic reaction of phenyl chlorofluoromethane and chlorodifluoromethane at very high temperature which results in mixtures of perfluoroethylene, xcex1,xcex2,xcex2-trifluorostyrene and difluorostilbene. Cohen et al., xcex1,xcex2,xcex2-Trifluorostyrene and xcex1-Chloro-xcex2,xcex2-Difluorostyrene, J.Am.Chem.Soc., 71(10):3439-3440 (1949) (xe2x80x9cCohenxe2x80x9d) discloses a synthesis of xcex1,xcex2,xcex2-trifluorostyrene which begins with a Friedel-Crafts reaction of trifluoroacetyl chloride with benzene in the presence of aluminum chloride.
Addition of perfluoroalkyl groups to aromatic compounds has been demonstrated. Tiers, Perfluoroalkylation of Aromatic Compounds, J.Am.Chem.Soc. 82:5513 (1960); U.S. Pat. No. 3,281,426; U.S. Pat. No. 3,271,441; Kamigata et al, Direct Perfluoroalkylation of Aromatic and Heteroaromatic Compounds, J. Chem Soc. Perkin Trans. 1:1339-1346 (1994). Addition of C4 or larger dichloroperfluoroalkyl groups to aromatic compounds and subsequent dechlorination to olefins has been demonstrated. Knunyants and Shokina, xcfx89-Phenylperfluoro-xcex1-Olefins and xcfx89-Phenylperfluoroalkanoic Acids, J.Acad.Sci.SSSR, Chem.Ser., pp. 68-71 (January, 1967).
Briefly, the present invention provides a process of reacting CFX2CFXI, wherein each X is independently F or Cl, provided that at least one X is Cl and at least one X is F, with an aromatic compound Ar to form (CFX2CFX)nxe2x80x94Ar, wherein n is 1, 2 or 3. This product may then be dechlorohalogenated to form (CFXxe2x95x90CF)nxe2x80x94Ar. The resulting xcex1,xcex2,xcex2-difluoro-xcex2-halo-ethenyl aromatic compounds, which are preferably xcex1,xcex2,xcex2-trifluoroethenyl aromatic compounds, may be polymerized or copolymerized and may be derivatized, e.g. by sulfonation, before dechlorohalogenation or after polymerization.
In another aspect, the present invention provides a reaction intermediate (CFCl2CF2)nxe2x80x94Ar, wherein X is F or Cl, n is 1, 2 or 3 and Ar is unsubstituted benzene.
In another aspect, the present invention provides a reaction intermediate (CFX2CFX)nxe2x80x94Ar, wherein each X is independently F or Cl, provided that at least one X of each (CFX2CFX) group is Cl and at least one X of each (CFX2CFX) group is F, wherein n is 1, 2 or 3 and wherein Ar is selected from the group consisting of monosubstituted benzene, disubstituted benzene and polysubstituted benzene bearing three or more substituents.
What has not been described in the art, and is provided by the present invention, is a relatively simple, inexpensive and effective synthetic route to xcex1,xcex2-difluoro-xcex2-halo-ethenyl aromatic compounds such as xcex1,xcex2,xcex2-trifluorostyrene and derivatives thereof. Furthermore, such a synthetic route involving addition to an aromatic compound bearing electronegative substituents has not been described.
In this application xe2x80x9cdechlorohalogenationxe2x80x9d refers to removal of a chlorine atom and another halogen atom, which may be chlorine or fluorine, from a molecule, e.g., removal of Cl and F from CF2ClCF2xe2x80x94Ar to form CF2xe2x95x90CFxe2x80x94Ar or removal of Cl and Cl from CF2ClCFClxe2x80x94Ar to form CF2xe2x95x90CFxe2x80x94Ar;
xe2x80x9csubstitutedxe2x80x9d means substituted by conventional substituents which do not interfere with the desired product, e.g., substituents can be alkyl, alkoxy, aryl, phenyl, halo (F, Cl, Br, I), cyano, nitro, etc; and
xe2x80x9ccarbonyl-attachedxe2x80x9d, xe2x80x9csulfonyl-attachedxe2x80x9d and xe2x80x9cphosphonyl-attachedxe2x80x9d refers to substituents that are attached to the substituted molecule at a carbonyl, sulfonyl or phosphonyl group (respectively) of the substituent.
As used herein, Ar represents an aromatic compound as specified or, where appropriate, a monovalent, divalent or trivalent moiety derived therefrom by removal of one, two or three hydrogens.
It is an advantage of the present invention to provide a relatively simple, inexpensive and low temperature synthetic route to xcex1,xcex2-difluoro-xcex2-halo-ethenyl aromatic compounds, including those bearing electronegative substituents and those used to fabricate ion exchange membranes or solid polymer electrolytes for use in electrochemical applications such as fuel cells.
The present invention provides a process of reacting CFX2CFXI, wherein each X is independently F or Cl, provided that at least one X is Cl and at least one X is F, with an aromatic compound Ar to form (CFX2CFX)nxe2x80x94Ar, wherein n is 1, 2 or 3. This product may then be dechlorohalogenated to form (CFXxe2x95x90CF)nxe2x80x94Ar. The resulting xcex1,xcex2-difluoro-xcex2-halo-ethenyl aromatic compounds, which are preferably xcex1,xcex2,xcex2-trifluoroethenyl aromatic compounds, may be polymerized or copolymerized and may be derivatized, e.g. by sulfonation, before dechlorhalogenation or after polymerization.
The aromatic starting compound may be any aromatic compound which will react in the present process. Such aromatic compounds must have at least one hydrogen bound to an aromatic carbon. Preferably, the aromatic compound is based on benzene, naphthalene, thiophene, phenanthrene or biphenyl. Most preferably the aromatic compound is based on benzene. The aromatic starting compound may be unsubstituted, monosubstituted, disubstituted or polysubstituted with three or more substituents. Preferred substituents include halogens, such as fluorine, mono- or polyhalogenated alkyl groups, which preferably contain 1-8 carbons and more preferably 1-3 carbons and are preferably perfluoroalkyl groups, aryl groups, halogenated oxa-alkyl groups, aryl ether groups, carbonyl-attached groups, such as fluorocarbonyl and keto aryl groups, sulfonyl-attached groups, such as fluorosulfonyl, aryl sulfones and aryl sulfonate esters, and phosphonyl-attached groups, such as difluorophosphonyl groups. Most-preferred substituents include phenyl, fluoro, perfluoroalkyl, in particular trifluoromethyl, and fluorosulfonyl (xe2x80x94SO2F). The aromatic starting compound may be made by any known process.
The use of aromatic starting compounds that are disubstituted, or polysubstituted with three or more substituents, may lead to syntheses of monomers, polymers and copolymers which were previously difficult or impossible to obtain. These include monomers, polymers and copolymers containing moieties such as 3,5-bis-(fluorosulfonyl)phenyl, 3,5-bis-(trifluoromethyl)phenyl, or 3-trifluoromethyl-5-fluorophenyl.
The iodoperhaloethane reactant is CFX2CFXI, wherein each X is independently F or Cl, provided that at least one X is Cl and at least one X is F. Thus the iodoperhaloethane reactant is selected from CF2ClCFClI, CF2ClCF2I, CF3CFClI, and CFCl2CF2I. CF2ClCFClI and CF3CFClI have the previously unrecognized advantage that they are more reactive with the aromatic compound as a result of the presence of a chlorine atom on the carbon bearing the iodine atom. The most preferred is CF2ClCFClI, which furthermore results in a product which is more readily dechlorohalogenated. CF2ClCF2I has the advantage that it can be made as a single isomer by addition of ICl to C2F4. The use of CF2ClCFClI, CF2ClCF2I or CF3CFClI results in trifluoroethenyl compounds after dechlorohalogenation. However, the use of CFCl2CF2I results in chlorodifluoroethenyl compounds after dechlorohalogenation, which do not polymerize as readily as trifluoroethenyl compounds.
The iodoperhaloethane reactant may be made by any suitable method. In one such method, ICl can be added to C2ClF3 at xe2x88x9210xc2x0 to 50xc2x0 C. to form a mixture of CF2ClCFClI and CCl2FCF2I. The mixture of isomers may be separated before reaction with the aromatic compound. The mixture may also be used as is in the reaction of the present invention without separation. It has been found that CF2ClCFClI is more reactive than CCl2FCF2I. Alternately, ICl can be added to C2F4 to form CF2ClCF2I. CF2ClCF2I and CF3CFClI can be made by the method of U.S. Pat. No. 3,006,973 by adding IF to CFxe2x95x90CFCl, wherein IF is generated in situ by the reaction of I2 and IF5.
It has been discovered that the aromatic compound and the iodoperhaloethane reactant will react to replace the iodine atom by the aryl group under the appropriate conditions of heat and pressure, preferably at 290xc2x0 C. or less, more preferably at 200xc2x0 C. or less, and even more preferably at 160xc2x0 C. or less, at the autogenous pressure generated in an autoclave or reaction vessel. Without wishing to be bound by theory, it is understood that the reaction proceeds by way of a free radical intermediate generated by removal of iodine from the iodoperhaloethane reactant. Lower temperatures and pressures may be achieved where additional means of generating free radicals are used. Such free radical generators include UV light and reagents such as tri-iron dodecacarbonyl and peroxides such as t-butyl peroxide.
A means of removing or trapping HI generated during the reaction can be used to advantage. HI generated during the reaction of the aromatic compound with CF2XCFXI attacks unreacted CF2XCFXI to form CF2XCFXH+I2. This effectively wastes half of the iodoperhaloethane reactant. Addition of an acid acceptor such as sodium acetate is one such means to remove or trap HI.
Iodine (I2) may be added to the initial reaction mixture to inhibit dimerization of the iodoperhaloethane reactant.
Preferably the reaction proceeds by addition of one iodoperhaloethane per aromatic compound to form products of the formula (CFX2CFX)xe2x80x94Ar. Since the perhaloethyl substituent is meta-directing, a second and third perhaloethane substituent may be added, resulting in the formation of bis- and tris-iodoperhaloethyl aromatic compounds of the formulae (CFX2CFX)2xe2x80x94Ar and (CFX2CFX)3xe2x80x94Ar. These may be recovered from the higher boiling fractions of the reaction mixture. Upon dechlorohalogenation, these compounds will yield (CF2xe2x95x90CF)2xe2x80x94Ar or (CF2xe2x95x90CF)3xe2x80x94Ar, which may be used as crosslinking monomers. The higher boiling products may also include heterosubstituted bis- and tris-iodoperhaloethyl aromatic compounds. For example, in the case where the iodoperhaloethane reactant used is a mixture of CF2ClCFClI and CCl2FCF2I, these products may include (CF2xe2x95x90CF)qxe2x80x94Arxe2x80x94(CFxe2x95x90CFCl)r, where q+r=2 or 3. These products may be useful, for example, to introduce into poly-xcex1,xcex2,xcex2-trifluorostyrene a styrene monomer with pendent unsaturated group, i.e. the less polymerizable (CFxe2x95x90CFCl) group.
The resulting product, (CFX2CFX)nxe2x80x94Ar, may be dechlorohalogenated (i.e. removal of X, X) to form (CFXxe2x95x90CF)nxe2x80x94Ar. Dechlorohalogenation may proceed by any suitable method, but is most advantageously performed by contacting the product with metallic zinc, preferably in the presence of a beneficial solvent, for example tetrahydrofuran (THF). This well known reaction was first used to prepare xcex1,xcex2,xcex2-trifluorostyrene by Cohen et al. Numerous variants have subsequently been disclosed.
The (CFX2CFX)nxe2x80x94Ar product may be derivatized by any suitable means prior to dechlorohalogenation. Derivatization includes addition of any suitable substituent, including halogenation, sulfonation, halosulfonation, nitration, etc.
Where the resulting product contains (CF2xe2x95x90CF)xe2x80x94 groups, it may be polymerized, including copolymerized, by any appropriate method such as disclosed in U.S. Pat. Nos. 5,602,185 and 5,773,480. The resulting polymer may be derivatized by any suitable means, including addition of any suitable substituent, including halogenation, sulfonation, halosulfonation, nitration, etc.
This invention is useful in the production of xcex1,xcex2,xcex2-trifluoroethenyl aromatic compounds including those that are used to fabricate ion exchange membranes or solid polymer electrolytes for use in electrochemical applications such as fuel cells.